Recent developments in advanced image displays, such as high definition TV (HDTV), have increased the demand for flat panel displays. One type of known flat panel display is a liquid crystal display (LCD). LCD's have several features and advantages which are not generally associated with other types of displays. For example, LCD's can operate in color, have relatively low-power demands, and also have high-speed performance relative to other types of displays such as electro-luminescence displays (ELDs), vacuum fluorescence displays (VFDs), and plasma display panels (PDPs).
Generally stated, LCDs can be characterized as either passive or active. Active type LCDs include pixels controlled by an active element such as a thin film transistor (TFT). Active type LCDs typically have much better response speed, visual display angle, color reproduction, and contrast compared to passive type LCDs. These characteristics make active type LCDs particularly suitable for use in HDTV, which generally requires high-resolution displays. In addition, these characteristics allow an active LCD to be thinner, lighter, and operate with lower power requirements. As a result, active type LCDs are also used as "notebook" computer monitors and in other display applications.
The active type of LCD is generally formed from several layers of materials; a thin film transistor (TFT) substrate layer, a color filter substrate layer, and a liquid crystal material layer positioned between the two substrates. Typically, the TFT substrate includes an intersecting array of spaced-apart gate lines and data lines. Generally stated, each intersecting area of a gate line and a data line includes a thin film transistor and a pixel electrode (typically a common-type electrode). In a conventional configuration, a protective layer, e.g., a nitride layer, together with pixel electrodes of ITO (indium tin oxide) material are formed on the gate lines. As such, the gate lines, the data lines, the thin film transistors and the pixel electrodes form the TFT substrate. Black matrices and color filters are formed on the color substrate layer. A protective layer and common electrodes of ITO material are also formed on the black matrices and the pixel electrodes to form the color filter substrate layer. The color filter substrate layer is positioned opposite the TFT substrate layer. The liquid crystal material is inserted into a space defined by the area between the TFT substrate and the color filter substrate layers, the space being on the order of about several .mu.m's.
The pixel or common electrodes of the TFT substrate and the color filter substrate include an orientation layer conventionally formed of a high-polymer material, such as polyimide, which is generally surface-treated by rubbing the material to obtain a thickness of about 500 to 1000 .ANG.. In addition, a polarizer film is typically attached to the outer surfaces of the TFT substrate and the color filter substrate. The orientation layer of the pixel electrodes functions to arrange molecules of the liquid crystal material on the TFT substrate and the color filter substrate such that they align in a predetermined direction. Polyimide resin can provide stability and durability in the orientation layer and is particularly suited to be used to form the orientation layer in the LCD display.
Examples of known processes used to obtain or form the orientation layer include organic high-polymer layer coating processes such as spin coating and flexographic technology. Generally stated, when the orientation layer is formed by spin coating technology, a pattern is formed and certain portions of the pattern are etched, which can be cumbersome and labor intensive work.
Recently, flexographic technology has been successfully used to apply the orientation layer. According to the flexographic technology, the orientation layer can be directly printed in a predetermined pattern without requiring any etching process. Generally described, the flexographic process can in theory be a substantially continuous process which uses a series of rollers to transfer a quantity of polyimide resin as a predetermined pattern onto the desired surface of the selected LCD layer (typically comprising a glass surface layer). Stated differently, the flexographic apparatus can be configured to automatically convey a plurality of glass panels sequentially through the process. The apparatus employs a special resin plate with a series of holding cells configured in a predetermined pattern to hold a quantity of polyimide resin (PI) processing solution. The resin plate is rotated and subsequently brought into direct contact with the glass panel surface to release the solution and transfer the predetermined pattern to form the orientation layer onto the surface. The glass panel is then heated to pre-cure the orientation layer.
Unfortunately, however, the flexographic process is not without problems. For example, as conventionally used, as will be discussed further herein, this process can disadvantageously be subject to frequent interruptions for cleaning, can have poor process yield, and can (intermittently) produce LCD's which have less than satisfactory display characteristics.